1. Field of the Invention
This invention relates to a coloring liquid containing a novel colorant compound, an ink tank using such a coloring liquid, a recording unit, a recording apparatus and a recording method.
2. Related Background Art
The widespread use of personal computers in ordinary households and the technological developments in the field of digital cameras are closely related to each other and have given rise to a synergetic effect of rapid popularization of hard copy techniques such as ink-jet recording for outputting electronic data to recording mediums.
While ink-jet recording can now provide high quality images that are comparable with images produced by silver halide photography due to the advancement of the ink-jet recording technology in recent years, various additional requirements have been posed to ink-jet recording including environmental stability of recorded images. Images printed on plain paper by means of inks prepared for ink-jet recording are accompanied by such problems that the image can become easily blurred and distorted by water, which problem by turn gives high priority to the requirement of water fastness. Thus, inks to be used for ink-jet recording are required to form images that are excellent in terms of both image quantity and water fastness. A high quality image refers to an image showing an enhanced degree of saturation and colorability.
Known techniques for providing high quality recorded images with cyan color by ink-jet recording includes one that uses as coloring agent a colorant compound having a triphenylmethane skeleton that shows a cyanic color tone. Generally, triphenylmethane compounds show a high molar absorption coefficient and ink that contains the colorant compound operates excellently in terms of color developability, vividness and colorability. It is known that the water fastness of printed products is improved by using inks containing a water-insoluble colorant. Either a pigment or an oil-soluble dye may be used as water-insoluble colorant.
For example, an ink composition containing a dye that has a triphenylmethane skeleton and shows a cyanic color tone has been proposed. (see Japanese Patent Application Laid-Open Application No. H08-333517). While the technique disclosed in the patent document can provide high quality recorded images, the colorant compound used in the ink composition is soluble in alcohol type solvents but poorly soluble in organic solvents to make its water fastness. insufficient.
The use of aqueous inks containing a pigment and a dye has been proposed to satisfy both the requirement of a high image quality and that of water fastness of images recorded by ink-jet recording (see Japanese Patent Application Laid-Open Application No. 2004-143336). The proposed technique is intended to meet the above requirements by using pigments that are characterized by high durability and high color density and dyes that show an enhanced degree of saturation. However, while an image printed by means of aqueous inks containing a pigment and a dye shows a high degree of water fastness, the saturation (color vividness) of the image is not satisfactory in terms of cyanic color tone as indicated by the L*a*b* colorimetric system. In other words, there is a demand for inks containing a colorant compound that are excellent in terms of cyanic color tone in order to improve the quality of images printed by ink-jet recording.